(S C,R S)-Bromido(N-{4-methyl-1-[(4-methylphenyl)sulfanyl]pentan-2-yl}-N′-(pyridin-2-yl)imidazol-2-ylidene)palladium(II) bromide

The molecule of the title NCNHCS pincer N-heterocyclic carbene palladium(II) complex, [PdBr(C21H25N3S)]Br, exhibits a slightly distorted square-planar coordination at the palladium(II) atom, with the five-membered chelate ring nearly planar. The six-membered chelate ring adopts an envelope conformation. Upon chelation, the sulfur atom becomes a stereogenic centre with an RS configuration induced by the chiral carbon of the precursor imidazolium salt.

The molecule of the title NC NHC S pincer N-heterocyclic carbene palladium(II) complex, [PdBr(C 21 H 25 N 3 S)]Br, exhibits a slightly distorted square-planar coordination at the palladium(II) atom, with the five-membered chelate ring nearly planar.The six-membered chelate ring adopts an envelope conformation.Upon chelation, the sulfur atom becomes a stereogenic centre with an R S configuration induced by the chiral carbon of the precursor imidazolium salt.There are intramolecular C-H� � �Br-Pd hydrogen bonds in the structure.The two interstitial Br atoms, as the counter-anion of the structure, are both located on crystallographic twofold axes and are connected to the complex cations via C-H� � �•Br hydrogen bonds.

Structure description
N-Heterocyclic carbenes (NHCs) have been widely used as ancillary ligands in coordination chemistry and organic catalysis due to their characteristic electronic properties and easy structural modification (Hopkinson et al., 2014;Gardiner et al., 2018).Introduction of a coordinating heteroatom functional group to the N-atom substituents of the NHCs leads to the formation of a potentially chelating ligand, and facilitates the formation of stable pincer NHC-metal complexes that can possess catalytic activities.Metal complexes containing heteroatom donors, such as P, N, O and S, have been synthesized, characterized and employed extensively as catalysts for a variety of organic transformations (Ahrens et al., 2006;Bierenstiel & Cross, 2011;Meyer et al., 2012;Peris & Crabtree, 2004).Our group has investigated the synthesis and catalytic performance of a series of chelating NHC-palladium complexes derived from natural amino alcohols (Yang et al., 2015(Yang et al., , 2023;;Yang, Zhang, Xiao & Mao, 2016;Yang, Zhang, Yuan et al., 2016;Meng et al., 2022).As part of our work on the study of NHC-metal complexes containing heteroatom-functionalized N-atom substituents, we present here the crystal structure of the title NC NHC S pincer NHC palladium(II) complex (Fig. 1).
Upon chelation, the sulfur atom becomes a stereogenic centre, resulting in the formation of molecules with an R S configuration.This can be attributed to the chiral induction of the chiral carbon C(5), which retains the same S configuration as in the precursor imidazolium salt.The environment of the sulfur atoms of the molecule is approximately triangular pyramidal.This is indicated by the bond angles C9-S1-Pd1, C15-S1-Pd1 and C9-S1-15, which were found to be 106.2(2), 111.0 (2), and 97.2 (3) � , respectively, with an average of 105.0 � .In the crystal, intra-and intermolecular C-H� � �Br hydrogen bonds occur (Table 1, Fig. 2).

Figure 1
The molecular structure of the title complex, shown with 50% probability displacement ellipsoids.

Special details
Geometry.All esds (except the esd in the dihedral angle between two l.s.planes) are estimated using the full covariance matrix.The cell esds are taken into account individually in the estimation of esds in distances, angles and torsion angles; correlations between esds in cell parameters are only used when they are defined by crystal symmetry.An approximate (isotropic) treatment of cell esds is used for estimating esds involving l.s.planes.Refinement.The H atoms on the carbons were positioned geometrically and constrained to ride on their parent atoms.C -H bond distances were constrained to 0.93 Å for aromatic and alkene C-H moieties, and to 0.98, 0.91 and 0.96 Å for aliphatic C-H, CH 2 and CH 3 moieties, respectively.Methyl CH 3 H atoms were allowed to rotate but not to tip to best fit the experimental electron density.U iso (H) values were set to a multiple of U eq (C) with 1.5 for CH 3 , and 1.2 for C-H and CH 2 units, respectively.

Table 2
Experimental details.